CN110732320B - Diesel engine tail gas oxidation catalyst and preparation method and application thereof - Google Patents
Diesel engine tail gas oxidation catalyst and preparation method and application thereof Download PDFInfo
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- CN110732320B CN110732320B CN201910970456.3A CN201910970456A CN110732320B CN 110732320 B CN110732320 B CN 110732320B CN 201910970456 A CN201910970456 A CN 201910970456A CN 110732320 B CN110732320 B CN 110732320B
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- oxidation catalyst
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- 230000003647 oxidation Effects 0.000 title claims abstract description 161
- 238000007254 oxidation reaction Methods 0.000 title claims abstract description 161
- 239000003054 catalyst Substances 0.000 title claims abstract description 148
- 238000002360 preparation method Methods 0.000 title claims abstract description 33
- 238000001179 sorption measurement Methods 0.000 claims abstract description 44
- 239000000919 ceramic Substances 0.000 claims abstract description 23
- 229910052878 cordierite Inorganic materials 0.000 claims abstract description 22
- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 claims abstract description 22
- 230000008859 change Effects 0.000 claims abstract description 20
- 239000011148 porous material Substances 0.000 claims abstract description 8
- 230000003247 decreasing effect Effects 0.000 claims abstract description 6
- 239000002002 slurry Substances 0.000 claims description 81
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 64
- 239000002131 composite material Substances 0.000 claims description 45
- 239000000377 silicon dioxide Substances 0.000 claims description 32
- -1 zirconium-aluminum-silicon Chemical compound 0.000 claims description 30
- 239000000463 material Substances 0.000 claims description 29
- 235000012239 silicon dioxide Nutrition 0.000 claims description 28
- 239000002994 raw material Substances 0.000 claims description 25
- 238000001035 drying Methods 0.000 claims description 20
- 229910001404 rare earth metal oxide Inorganic materials 0.000 claims description 18
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 17
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 claims description 16
- 239000002245 particle Substances 0.000 claims description 16
- 238000000498 ball milling Methods 0.000 claims description 15
- 239000008367 deionised water Substances 0.000 claims description 15
- 229910021641 deionized water Inorganic materials 0.000 claims description 15
- 238000005303 weighing Methods 0.000 claims description 15
- 239000012752 auxiliary agent Substances 0.000 claims description 14
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical class O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 claims description 13
- 239000010953 base metal Substances 0.000 claims description 11
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 10
- 238000007664 blowing Methods 0.000 claims description 10
- 229910000420 cerium oxide Inorganic materials 0.000 claims description 10
- 238000007598 dipping method Methods 0.000 claims description 10
- 229910044991 metal oxide Inorganic materials 0.000 claims description 10
- 150000004706 metal oxides Chemical class 0.000 claims description 10
- 229910000510 noble metal Inorganic materials 0.000 claims description 10
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 claims description 10
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims description 8
- 229910021536 Zeolite Inorganic materials 0.000 claims description 8
- 239000010457 zeolite Substances 0.000 claims description 8
- 238000000034 method Methods 0.000 claims description 7
- 238000000746 purification Methods 0.000 claims description 7
- 229910052684 Cerium Inorganic materials 0.000 claims description 6
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 6
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 claims description 6
- 230000007423 decrease Effects 0.000 claims description 6
- 229910052748 manganese Inorganic materials 0.000 claims description 6
- 239000011572 manganese Substances 0.000 claims description 6
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 6
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 5
- 239000004480 active ingredient Substances 0.000 claims description 5
- 238000001816 cooling Methods 0.000 claims description 5
- 238000000151 deposition Methods 0.000 claims description 5
- 229910052742 iron Inorganic materials 0.000 claims description 5
- 230000007935 neutral effect Effects 0.000 claims description 5
- 229910017604 nitric acid Inorganic materials 0.000 claims description 5
- 238000002390 rotary evaporation Methods 0.000 claims description 5
- 238000002791 soaking Methods 0.000 claims description 5
- 238000005406 washing Methods 0.000 claims description 5
- 229910052763 palladium Inorganic materials 0.000 claims description 4
- 229910052703 rhodium Inorganic materials 0.000 claims description 4
- 239000010948 rhodium Substances 0.000 claims description 4
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 claims description 4
- 229910052697 platinum Inorganic materials 0.000 claims description 3
- 239000010970 precious metal Substances 0.000 claims description 3
- 239000003463 adsorbent Substances 0.000 claims 1
- 238000006555 catalytic reaction Methods 0.000 abstract description 12
- 230000003197 catalytic effect Effects 0.000 abstract description 7
- 229910002091 carbon monoxide Inorganic materials 0.000 abstract description 5
- 238000013329 compounding Methods 0.000 abstract description 3
- 238000013461 design Methods 0.000 abstract description 3
- 239000007789 gas Substances 0.000 description 35
- 238000011068 loading method Methods 0.000 description 10
- 230000000052 comparative effect Effects 0.000 description 8
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 6
- 238000005516 engineering process Methods 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 5
- HSJPMRKMPBAUAU-UHFFFAOYSA-N cerium(3+);trinitrate Chemical compound [Ce+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O HSJPMRKMPBAUAU-UHFFFAOYSA-N 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000003344 environmental pollutant Substances 0.000 description 4
- 238000009472 formulation Methods 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 231100000719 pollutant Toxicity 0.000 description 4
- OERNJTNJEZOPIA-UHFFFAOYSA-N zirconium nitrate Chemical compound [Zr+4].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O OERNJTNJEZOPIA-UHFFFAOYSA-N 0.000 description 4
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- BNGXYYYYKUGPPF-UHFFFAOYSA-M (3-methylphenyl)methyl-triphenylphosphanium;chloride Chemical compound [Cl-].CC1=CC=CC(C[P+](C=2C=CC=CC=2)(C=2C=CC=CC=2)C=2C=CC=CC=2)=C1 BNGXYYYYKUGPPF-UHFFFAOYSA-M 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000033228 biological regulation Effects 0.000 description 2
- 239000000969 carrier Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000000975 co-precipitation Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- FYDKNKUEBJQCCN-UHFFFAOYSA-N lanthanum(3+);trinitrate Chemical compound [La+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O FYDKNKUEBJQCCN-UHFFFAOYSA-N 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- GPNDARIEYHPYAY-UHFFFAOYSA-N palladium(ii) nitrate Chemical compound [Pd+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O GPNDARIEYHPYAY-UHFFFAOYSA-N 0.000 description 2
- NWAHZABTSDUXMJ-UHFFFAOYSA-N platinum(2+);dinitrate Chemical compound [Pt+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O NWAHZABTSDUXMJ-UHFFFAOYSA-N 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000006722 reduction reaction Methods 0.000 description 2
- VXNYVYJABGOSBX-UHFFFAOYSA-N rhodium(3+);trinitrate Chemical compound [Rh+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VXNYVYJABGOSBX-UHFFFAOYSA-N 0.000 description 2
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 2
- 229910001868 water Inorganic materials 0.000 description 2
- 229910018557 Si O Inorganic materials 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- OBNDGIHQAIXEAO-UHFFFAOYSA-N [O].[Si] Chemical compound [O].[Si] OBNDGIHQAIXEAO-UHFFFAOYSA-N 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 1
- 238000010531 catalytic reduction reaction Methods 0.000 description 1
- 230000009920 chelation Effects 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000013066 combination product Substances 0.000 description 1
- 229940127555 combination product Drugs 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000002808 molecular sieve Substances 0.000 description 1
- 239000002086 nanomaterial Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- FVZVCSNXTFCBQU-UHFFFAOYSA-N phosphanyl Chemical group [PH2] FVZVCSNXTFCBQU-UHFFFAOYSA-N 0.000 description 1
- 125000005499 phosphonyl group Chemical group 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 125000002924 primary amino group Chemical group [H]N([H])* 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Inorganic materials [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 1
- 239000004071 soot Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 125000003396 thiol group Chemical class [H]S* 0.000 description 1
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- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/922—Mixtures of carbon monoxide or hydrocarbons and nitrogen oxides
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- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
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- B01J37/341—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation
- B01J37/343—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation of ultrasonic wave energy
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Abstract
The invention discloses a diesel engine tail gas oxidation catalyst, which takes cordierite honeycomb ceramics as a carrier, wherein an adsorption layer is coated on the surface of a pore channel of the carrier, and a first oxidation catalyst layer and a second oxidation catalyst layer are coated on the adsorption layer; the concentration of the first active component in the first oxidation catalysis layer is in gradient decreasing change along the airflow direction on the surface of the carrier, and the concentration of the second active component in the second oxidation catalysis layer is in gradient increasing change along the airflow direction on the surface of the carrier. The oxidation catalyst disclosed by the invention is reasonable in structure design, and has the advantages of low cost and high catalytic efficiency due to the optimized compounding of all components, and can meet the requirement of simultaneous oxidation treatment of tail gas components of diesel engines such as HC, CO, PM and NOx, the tail gas treatment efficiency is improved, and the occupied space of the traditional diesel engine tail gas treatment device is reduced. The invention also discloses a preparation method and application of the diesel engine tail gas oxidation catalyst.
Description
Technical Field
The invention relates to the technical field of catalysts, in particular to a diesel engine tail gas oxidation catalyst and a preparation method and application thereof.
Background
The exhaust gas of the diesel engine contains various pollutants such as CO, HC, NOx, Particulate Matters (PM) and the like, and along with the continuous increase of the output and sales volume of the diesel engine, the pollution of the exhaust gas of the diesel engine to the atmospheric environment is more and more serious, the emission of the pollutants accounts for more than 50 percent of the emission of automobiles, and the prevention and treatment work of the pollution of the exhaust gas of the diesel engine is urgent.
With the continuous upgrading of emission regulations, the requirements cannot be met only by means of combustion purification technology in an engine, and an exhaust aftertreatment system becomes a necessary system for a diesel engine to meet the strict emission regulations above national IV. The technology for after-treatment of diesel vehicle emissions is more complex and more difficult than gasoline engines due to the limitation of pollutant species and emission characteristics, and includes oxidation catalyst (DOC) technology, particulate filter (DPF) technology, Selective Catalytic Reduction (SCR) technology, and combination product technology.
The diesel oxidation catalyst product is complex and is considered from a functional point of view: including CO/HC oxidation type catalysts, soot oxidation catalysts, NH3 oxidation catalysts, and the like; from the application range point of view: including oxidation catalysts for automobiles, oxidation catalysts for stationary source diesel engines, and the like; from the viewpoint of the catalyst support material: including honeycomb ceramic carriers and metal honeycomb carriers, etc. How to synchronously and efficiently purify harmful pollutants such as CO, HC, NOx, particulate matters and the like contained in the tail gas of the diesel engine is a problem which troubles the technical personnel in the field and needs to be solved urgently.
Disclosure of Invention
In view of the defects of the prior art, the invention provides the diesel engine tail gas oxidation catalyst which is reasonable in structure design, has the advantages of low cost and high catalytic efficiency by optimizing and compounding all components, and can meet the requirement of simultaneous oxidation treatment of HC, CO, PM, NOx and other diesel engine tail gas components.
The invention also provides a preparation method of the diesel engine tail gas oxidation catalyst, which effectively prevents the loss of noble metals and improves the loading and dispersion of active components on the surface of a carrier.
The invention also provides application of the diesel engine tail gas oxidation catalyst to purification treatment of diesel engine tail gas.
In order to achieve the above purposes, the technical scheme adopted by the invention is as follows:
a diesel engine tail gas oxidation catalyst takes cordierite honeycomb ceramics as a carrier, an adsorption layer is coated on the surface of a pore channel of the carrier, and a first oxidation catalyst layer and a second oxidation catalyst layer are coated on the adsorption layer; the concentration of the first active component in the first oxidation catalysis layer is in gradient decreasing change along the airflow direction on the surface of the carrier, and the concentration of the second active component in the second oxidation catalysis layer is in gradient increasing change along the airflow direction on the surface of the carrier.
Preferably, the mass ratio of the support, the adsorption layer, the first oxidation catalyst layer, and the second oxidation catalyst layer is 80 to 98: 1-15: 0.5-5: 0.5 to 5.
The first active component concentration is the percentage of the first active component in the total mass of the first oxidation catalyst layer, and the first active component concentration decreases in a gradient manner along the airflow direction on the surface of the carrier, and can be specifically described as that the mass percentage concentration of the first active component on the side close to the airflow inlet of the carrier is higher than that on the side close to the airflow outlet of the carrier; when diesel exhaust flows into the inlet side of the carrier, the first active component with high concentration at the inlet side of the carrier oxidizes tail gas components such as free C, CO, NO, SOF and the like adsorbed by the adsorption layer into CO2 and NO2 in a low-temperature state.
Similarly, the second active component concentration refers to the percentage of the second active component in the total mass of the second oxidation catalysis layer, and the second active component concentration increases and changes in a gradient manner along the airflow direction on the surface of the carrier, and can be specifically described as that the mass percentage concentration of the second active component on the side close to the airflow outlet of the carrier is higher relative to that on the side close to the airflow inlet of the carrier; when the tail gas of the diesel engine flows to be close to the outlet side of the carrier, the second active component with high concentration at the outlet side of the carrier further oxidizes PM by using NO2 obtained after the oxidation at the inlet side of the carrier under a high-temperature state, and simultaneously generates H2O, CO2 and N2 which are finally discharged.
The cordierite honeycomb ceramic carrier plays a role in filtering tail gas particles, and the adsorption layer coated on the surface of a carrier pore channel is beneficial to adsorbing harmful gas components in tail gas such as HC, SOF, NOx and the like under a low-temperature condition; the concentration gradient of the first active component is reduced, HC, CO and NO tail gas components adsorbed at the inlet of the carrier are subjected to centralized and efficient catalytic oxidation, the concentration gradient of the second active component is increased, and PM adsorbed by NO2 oxidized and obtained by the oxidation of the first active component can be used at the outlet of the carrier, so that H2O, CO2 and N2 are generated simultaneously, and the effect of simultaneously oxidizing and removing multiple components of tail gas of a diesel engine is achieved.
Preferably, the adsorption layer is a cage-type silsesquioxane modified zeolite layer.
The cage type silsesquioxane, POSS for short, is an inorganic core consisting of a silicon-oxygen framework alternately connected by Si-O, and has a general formula (RSiO3/2) n, wherein R is an active group connected by eight apical angle Si atoms. In a specific embodiment of the present invention, the active group is selected from at least one of phosphino, phosphonyl, amino, mercapto, hydroxyl, and carboxyl. The active group has a metal chelating function, and more preferably, an active group of amino or mercapto cage-type silsesquioxane is selected.
Zeolite is used as one kind of molecular sieve, has regular pore channel structure and good adsorption performance, and is widely applied to the fields of catalysis and adsorption. The adsorption of zeolite to molecules is a physical change process, and after modification treatment of the cage-type silsesquioxane, a large number of active groups carried on the cage-type silsesquioxane generate chelation with metals, so that the dispersion and loading of the first active component and the second active component on the surface of the adsorption layer are enhanced, the catalytic activity of the oxidation catalyst is further improved, and the oxidation catalyst has a higher tail gas purification effect.
Preferably, the first oxidation catalyst layer uses a noble metal as a first active component, a rare earth metal oxide and silica as auxiliaries, and a zirconium-aluminum-silicon composite oxide as a loading material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 1-3: 0.5-2: 20.
preferably, the noble metal is at least one of platinum, palladium and rhodium.
Preferably, the second oxidation catalyst layer uses base metal oxide as a second active component, rare earth metal oxide and silicon dioxide as auxiliaries, and zirconium-aluminum-silicon composite oxide as a loading material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 1-3: 0.5-2: 20.
preferably, the base metal oxide is at least one of an iron-based perovskite-type composite oxide, a manganese-based perovskite-type composite oxide, and a cerium-based perovskite-type composite oxide.
The perovskite type composite oxide ABO3 is an inorganic non-metallic material with unique physical properties and chemical properties, the perovskite type composite oxide is doped and modified by soluble salts containing iron, manganese and cerium, so that the iron-based perovskite type composite oxide, the manganese-based perovskite type composite oxide and the cerium-based perovskite type composite oxide can be obtained, and the oxidation catalyst has excellent catalytic performance for NOx at high temperature due to the crystal defect structure and performance formed after doping.
Preferably, the rare earth metal oxide is at least one of cerium oxide and lanthanum oxide.
A corresponding method of making a diesel exhaust oxidation catalyst as described above, comprising the steps of:
s1: pretreatment of a carrier: placing a cordierite honeycomb ceramic carrier in a nitric acid solution for soaking for 3h, then washing with ultrasonic waves to be neutral, then drying in a drying oven at 110-120 ℃ for 1.5h, then placing in a muffle furnace for roasting at 600-800 ℃ for 2-3 h, and finally naturally cooling to obtain a pretreated cordierite honeycomb ceramic carrier;
s2: preparation of adsorption layer slurry: according to the mass ratio of zeolite, cage-type silsesquioxane to deionized water of 1-3: 0.5 to 2: 20, weighing the raw materials, uniformly ball-milling in a planetary ball mill, and controlling ball-milled particles D90 to be 5-15 mu m to prepare an adsorption layer slurry;
s3: preparation of a first oxidation catalyst layer slurry: according to the mass ratio of the noble metal, the rare earth metal oxide, the silicon dioxide, the zirconium-aluminum-silicon composite oxide and the deionized water of 1-3: 0.1-1.5: 0.1-1: 20: weighing the raw materials by 50, uniformly ball-milling in a planetary ball mill, and controlling the ball-milled particles D90 to be 1-5 mu m to prepare a first oxidation catalyst layer slurry;
in the preparation process, the raw material sources of the noble metal are selected from platinum nitrate, palladium nitrate and rhodium nitrate, the raw material sources of the rare earth metal oxide cerium oxide and lanthanum oxide are respectively selected from cerium nitrate and lanthanum nitrate, the raw material source of the silicon dioxide is selected from cage type silsesquioxane, and the zirconium-aluminum-silicon composite oxide is prepared from zirconium nitrate, aluminum nitrate and silica sol through coprecipitation;
s4: preparation of a second oxidation catalyst layer slurry: according to the mass ratio of base metal oxide, rare earth metal oxide, silicon dioxide, zirconium-aluminum-silicon composite oxide and deionized water of 1-3: 0.1-1.5: 0.1-1: 20: weighing the raw materials 50, uniformly ball-milling in a planetary ball mill, and controlling the ball-milled particles D90 to be 1-5 mu m to prepare second oxidation catalyst layer slurry;
in the preparation process, the raw material sources of base metal oxides are selected from platinum nitrate, palladium nitrate and rhodium nitrate, the raw material sources of rare earth metal oxides cerium oxide and lanthanum oxide are respectively selected from cerium nitrate and lanthanum nitrate, the raw material source of silicon dioxide is selected from cage-type silsesquioxane, and the zirconium-aluminum-silicon composite oxide is prepared from zirconium nitrate, aluminum nitrate and silica sol through coprecipitation;
s5: preparation of oxidation catalyst: dipping the cordierite honeycomb ceramic carrier obtained in the step S1 in the adsorption layer slurry prepared in the step S2, and finishing the dipping operation by an ultrasonic-assisted rotary evaporation method; blowing with compressed air and drying at 110 deg.c to constant weight; and taking out and placing the slurry into a sealed container, respectively arranging an inlet and an outlet at two ends of the sealed container along the airflow direction on the surface of the carrier, simultaneously or sequentially introducing the first oxidation catalyst layer slurry prepared in the step S3 and the second oxidation catalyst layer slurry prepared in the step S4 at the inlets, controlling the flow rate of the first oxidation catalyst layer slurry to gradually decrease from fast to slow, controlling the flow rate of the second oxidation catalyst layer slurry to gradually increase from slow to fast, depositing the slurry on the adsorption layer, blowing the slurry by compressed air again, drying the slurry to constant weight at 110 ℃, and finally roasting the slurry for 1 to 3 hours at 600 to 750 ℃ to obtain the oxidation catalyst with active ingredient concentration gradient change.
In the preparation process of the first oxidation catalyst layer and the second oxidation catalyst layer, cage-type silsesquioxane is added as a silicon source of silicon dioxide, so that the silicon dioxide has a bonding effect; meanwhile, due to the characteristics of the organic-inorganic hybrid nanostructure of the cage-type silsesquioxane, the cage-type silsesquioxane plays a good role in dispersion when the initial slurry is prepared, and the temperature is gradually increased for sintering to obtain high-density silicon dioxide, so that the adhesive force between the catalytic coating and the carrier is enhanced.
Correspondingly, the oxidation catalyst is applied to the purification of the tail gas of the diesel engine.
The invention has the beneficial effects that:
according to the diesel engine tail gas oxidation catalyst, the prepared oxidation catalyst has a synergistic oxidation effect by the characteristic that the first active component and the second active component respectively have a concentration gradient change relationship in the first oxidation catalyst layer and the second oxidation catalyst layer, and can simultaneously purify harmful tail gas components such as HC, CO, PM and NOx contained in tail gas.
In the preparation process of the first oxidation catalyst layer and the second oxidation catalyst layer, direct impregnation loading is adopted, so that loss of precious metals is easily caused.
According to the invention, through the optimized compounding of base metal and precious metal active components and the reasonable design of the catalyst structure, the preparation cost of the catalyst is reduced, the conversion rate of CO and HC in the tail gas of the diesel engine reaches 96%, the PM purification rate reaches more than 60%, and the reduction rate of NOx reaches more than 50%.
Detailed Description
The following description is presented to disclose the invention so as to enable any person skilled in the art to practice the invention. The preferred embodiments in the following description are given by way of example only, and other obvious variations will occur to those skilled in the art.
Example 1
In the diesel engine exhaust gas oxidation catalyst of the embodiment, cordierite honeycomb ceramic is used as a carrier of the oxidation catalyst, a cage-type silsesquioxane modified zeolite layer is coated on the surfaces of pore channels of the carrier, and a first oxidation catalyst layer and a second oxidation catalyst layer are coated on an adsorption layer; the concentration of the first active component in the first oxidation catalysis layer is in gradient decreasing change along the airflow direction on the surface of the carrier, and the concentration of the second active component in the second oxidation catalysis layer is in gradient increasing change along the airflow direction on the surface of the carrier.
The mass ratio of the carrier to the adsorption layer to the first and second oxidation catalyst layers is 90: 5: 2.5: 2.5.
The first oxidation catalyst layer takes platinum as a first active component, cerium oxide and silicon dioxide as auxiliaries and a zirconium-aluminum-silicon composite oxide as a loading material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 2: 1: 20.
the second oxidation catalyst layer takes an iron-based perovskite type composite oxide as a second active component, takes cerium oxide and silicon dioxide as auxiliaries and takes a zirconium-aluminum-silicon composite oxide as a load material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 2: 1: 20.
in the zirconium aluminum silicon composite oxide, the weight ratio of zirconia, alumina and silica is 2.5: 2: 0.3.
a corresponding method of making a diesel exhaust oxidation catalyst as described above, comprising the steps of:
s1: pretreatment of a carrier: placing a cordierite honeycomb ceramic carrier in a nitric acid solution for soaking for 3h, then washing by ultrasonic to be neutral, then drying for 1.5h in a drying box at 110 ℃, then placing in a muffle furnace for roasting for 3h at 600 ℃, and finally naturally cooling to obtain a pretreated cordierite honeycomb ceramic carrier;
s2: preparation of adsorption layer slurry: according to the mass ratio of zeolite, cage type silsesquioxane and deionized water of 2: 1: 20, weighing the raw materials, uniformly ball-milling in a planetary ball mill, and controlling ball-milled particles D90 to be 10 microns to prepare adsorption layer slurry;
s3: preparation of a first oxidation catalyst layer slurry: according to the mass ratio of noble metal, rare earth metal oxide, silicon dioxide, zirconium-aluminum-silicon composite oxide and deionized water of 2: 0.5: 0.5: 20: weighing the raw materials 50, uniformly ball-milling in a planetary ball mill, and controlling ball-milled particles D90 to be 3 mu m to prepare first oxidation catalyst layer slurry;
s4: preparation of a second oxidation catalyst layer slurry: according to the mass ratio of base metal oxide, rare earth metal oxide, silicon dioxide, zirconium-aluminum-silicon composite oxide and deionized water of 2: 0.5: 0.5: 20: weighing the raw materials 50, uniformly ball-milling in a planetary ball mill, and controlling the ball-milled particles D90 to be 3 mu m to prepare second oxidation catalyst layer slurry;
s5: preparation of oxidation catalyst: dipping the cordierite honeycomb ceramic carrier obtained in the step S1 in the adsorption layer slurry prepared in the step S2, and finishing the dipping operation by an ultrasonic-assisted rotary evaporation method; blowing with compressed air and drying at 110 deg.c to constant weight; taking out and placing the slurry in a sealed container, respectively arranging an inlet and an outlet at two ends of the sealed container along the airflow direction on the surface of the carrier, simultaneously or sequentially introducing the first oxidation catalyst layer slurry prepared in the step S3 and the second oxidation catalyst layer slurry prepared in the step S4 at the inlet, controlling the flow rate of the first oxidation catalyst layer slurry to gradually decrease from fast to slow, controlling the flow rate of the second oxidation catalyst layer slurry to gradually increase from slow to fast, depositing the slurry on the adsorption layer, blowing the slurry by compressed air again, drying the slurry to constant weight at 110 ℃, and finally roasting the slurry for 2 hours at 700 ℃ to obtain the oxidation catalyst with active ingredient concentration gradient change.
Example 2
In the diesel engine exhaust gas oxidation catalyst of the embodiment, cordierite honeycomb ceramic is used as a carrier of the oxidation catalyst, a cage-type silsesquioxane modified zeolite layer is coated on the surfaces of pore channels of the carrier, and a first oxidation catalyst layer and a second oxidation catalyst layer are coated on an adsorption layer; the concentration of the first active component in the first oxidation catalysis layer is in gradient decreasing change along the airflow direction on the surface of the carrier, and the concentration of the second active component in the second oxidation catalysis layer is in gradient increasing change along the airflow direction on the surface of the carrier.
The mass ratio of the carrier to the adsorption layer to the first and second oxidation catalyst layers is 80: 10: 5: 5.
the first oxidation catalyst layer takes palladium as a first active component, takes cerium oxide and silicon dioxide as auxiliaries and takes a zirconium-aluminum-silicon composite oxide as a loading material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 1: 2: 20.
the second oxidation catalyst layer takes manganese-based perovskite type composite oxide as a second active component, cerium oxide and silicon dioxide as auxiliaries and zirconium-aluminum-silicon composite oxide as a load material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 1: 2: 20.
in the zirconium-aluminum-silicon composite oxide, the weight ratio of zirconia, alumina and silica is 1.8: 1.5: 0.1.
a corresponding method of making a diesel exhaust oxidation catalyst as described above, comprising the steps of:
s1: pretreatment of a carrier: placing a cordierite honeycomb ceramic carrier in a nitric acid solution for soaking for 3h, then washing by ultrasonic to be neutral, then drying for 1.5h in a drying box at 120 ℃, then placing in a muffle furnace for roasting for 3h at 800 ℃, and finally naturally cooling to obtain a pretreated cordierite honeycomb ceramic carrier;
s2: preparation of adsorption layer slurry: according to the mass ratio of zeolite, cage type silsesquioxane and deionized water of 1: 0.5: 20, weighing the raw materials, uniformly ball-milling in a planetary ball mill, and controlling ball-milled particles D90 to be 5 microns to prepare an adsorption layer slurry;
s3: preparation of a first oxidation catalyst layer slurry: according to the mass ratio of noble metal, rare earth metal oxide, silicon dioxide, zirconium-aluminum-silicon composite oxide and deionized water of 1: 1.5: 0.5: 20: weighing the raw materials 50, uniformly ball-milling in a planetary ball mill, and controlling the ball-milled particles D90 to be 1 mu m to prepare a first oxidation catalyst layer slurry;
s4: preparation of a second oxidation catalyst layer slurry: according to the mass ratio of base metal oxide, rare earth metal oxide, silicon dioxide, zirconium-aluminum-silicon composite oxide and deionized water of 1: 1.5: 0.5: 20: 50, weighing the raw materials, uniformly ball-milling in a planetary ball mill, and controlling the ball-milled particles D90 to be 1 mu m to prepare second oxidation catalyst layer slurry;
s5: preparation of oxidation catalyst: dipping the cordierite honeycomb ceramic carrier obtained in the step S1 in the adsorption layer slurry prepared in the step S2, and finishing the dipping operation by an ultrasonic-assisted rotary evaporation method; blowing with compressed air and drying at 110 deg.c to constant weight; taking out and placing the slurry in a sealed container, respectively arranging an inlet and an outlet at two ends of the sealed container along the airflow direction on the surface of the carrier, simultaneously or sequentially introducing the first oxidation catalyst layer slurry prepared in the step S3 and the second oxidation catalyst layer slurry prepared in the step S4 at the inlet, controlling the flow rate of the first oxidation catalyst layer slurry to gradually decrease from fast to slow, controlling the flow rate of the second oxidation catalyst layer slurry to gradually increase from slow to fast, depositing the slurry on the adsorption layer, blowing the slurry by compressed air again, drying the slurry to constant weight at 110 ℃, and finally roasting the slurry for 3 hours at 600 ℃ to obtain the oxidation catalyst with active ingredient concentration gradient change.
Example 3
In the diesel engine exhaust gas oxidation catalyst of the embodiment, cordierite honeycomb ceramic is used as a carrier of the oxidation catalyst, a cage-type silsesquioxane modified zeolite layer is coated on the surfaces of pore channels of the carrier, and a first oxidation catalyst layer and a second oxidation catalyst layer are coated on an adsorption layer; the concentration of the first active component in the first oxidation catalysis layer is in gradient decreasing change along the airflow direction on the surface of the carrier, and the concentration of the second active component in the second oxidation catalysis layer is in gradient increasing change along the airflow direction on the surface of the carrier.
The mass ratio of the carrier to the adsorption layer to the first and second oxidation catalyst layers is 98: 1: 0.5: 0.5.
The first oxidation catalyst layer takes rhodium as a first active component, lanthanum oxide and silicon dioxide as auxiliaries and a zirconium-aluminum-silicon composite oxide as a loading material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 3: 1.5: 20.
the second oxidation catalyst layer takes a cerium-based perovskite type composite oxide as a second active component, lanthanum oxide and silicon dioxide as auxiliaries and a zirconium-aluminum-silicon composite oxide as a load material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 3: 1.5: 20.
in the zirconium aluminum silicon composite oxide, the weight ratio of zirconia, alumina and silica is 3.5: 3: 0.5.
a corresponding method of making a diesel exhaust oxidation catalyst as described above, comprising the steps of:
s1: pretreatment of a carrier: placing a cordierite honeycomb ceramic carrier in a nitric acid solution for soaking for 3h, then washing by ultrasonic to be neutral, then drying for 1.5h in a drying box at 120 ℃, then placing in a muffle furnace for roasting for 3h at 700 ℃, and finally naturally cooling to obtain a pretreated cordierite honeycomb ceramic carrier;
s2: preparation of adsorption layer slurry: according to the mass ratio of zeolite, cage type silsesquioxane and deionized water of 3: 2: 20, weighing the raw materials, uniformly ball-milling in a planetary ball mill, and controlling ball-milled particles D90 to be 15 microns to prepare an adsorption layer slurry;
s3: preparation of a first oxidation catalyst layer slurry: according to the mass ratio of noble metal, rare earth metal oxide, silicon dioxide, zirconium-aluminum-silicon composite oxide and deionized water of 3: 1: 0.5: 20: weighing the raw materials 50, uniformly ball-milling in a planetary ball mill, and controlling the ball-milled particles D90 to be 5 microns to prepare a first oxidation catalyst layer slurry;
s4: preparation of a second oxidation catalyst layer slurry: according to the mass ratio of base metal oxide, rare earth metal oxide, silicon dioxide, zirconium-aluminum-silicon composite oxide and deionized water of 3: 1: 0.5: 20: weighing the raw materials 50, uniformly ball-milling in a planetary ball mill, and controlling the ball-milled particles D90 to be 5 microns to prepare second oxidation catalyst layer slurry;
s5: preparation of oxidation catalyst: dipping the cordierite honeycomb ceramic carrier obtained in the step S1 in the adsorption layer slurry prepared in the step S2, and finishing the dipping operation by an ultrasonic-assisted rotary evaporation method; blowing with compressed air and drying at 110 deg.c to constant weight; and taking out and placing the slurry into a sealed container, respectively arranging an inlet and an outlet at two ends of the sealed container along the airflow direction on the surface of the carrier, simultaneously or sequentially introducing the first oxidation catalyst layer slurry prepared in the step S3 and the second oxidation catalyst layer slurry prepared in the step S4 at the inlets, controlling the flow rate of the first oxidation catalyst layer slurry to gradually decrease from fast to slow, controlling the flow rate of the second oxidation catalyst layer slurry to gradually increase from slow to fast, depositing the slurry on the adsorption layer, blowing the slurry by compressed air again, drying the slurry to constant weight at 110 ℃, and finally roasting the slurry at 680 ℃ for 3 hours to obtain the oxidation catalyst with active ingredient concentration gradient change.
Example 4
The diesel engine exhaust gas oxidation catalyst of the present example is basically similar to example 1 in the raw material formulation and the preparation method, and mainly differs therefrom in that the mass ratio of the carrier, the adsorption layer, the first oxidation catalyst layer, and the second oxidation catalyst layer is 85: 8: 3.5: 3.5.
the first oxidation catalyst layer takes palladium as a first active component, lanthanum oxide and silicon dioxide as auxiliaries and a zirconium-aluminum-silicon composite oxide as a loading material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 1.5: 0.8: 20.
the second oxidation catalyst layer takes manganese-based perovskite type composite oxide as a second active component, lanthanum oxide and silicon dioxide as auxiliaries and zirconium-aluminum-silicon composite oxide as a load material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 2.5: 1.5: 20.
example 5
The diesel engine exhaust gas oxidation catalyst of the present example is basically similar to example 1 in the raw material formulation and the preparation method, and mainly differs therefrom in that the mass ratio of the carrier, the adsorption layer, the first oxidation catalyst layer, and the second oxidation catalyst layer is 93: 4: 1.5: 1.5.
the first oxidation catalyst layer takes rhodium as a first active component, takes cerium oxide and silicon dioxide as auxiliaries and takes a zirconium-aluminum-silicon composite oxide as a loading material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 2.5: 1.5: 20.
the second oxidation catalyst layer takes a cerium-based perovskite type composite oxide as a second active component, takes cerium oxide and silicon dioxide as auxiliaries and takes a zirconium-aluminum-silicon composite oxide as a load material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 1.5: 2: 20.
comparative example 1
The diesel exhaust oxidation catalyst of this comparative example was substantially similar to example 1 in the raw material formulation and the production method, and was mainly different in that the first active component concentration in the first oxidation catalyst layer and the second active component concentration in the second oxidation catalyst layer did not change in a gradient in the gas flow direction on the surface of the support.
Comparative example 2
The diesel exhaust oxidation catalyst of this comparative example was substantially similar in raw material formulation and preparation method to example 1, except that the adsorption layer was a zeolite layer which was not modified with cage-type silsesquioxane.
The oxidation catalysts prepared in examples 1 to 5 and comparative examples 1 to 2 were applied to a diesel engine exhaust gas treatment device, and the exhaust gas was subjected to corresponding performance tests, and the performance results are shown in table 1:
the catalytic performance of the oxidation catalysts prepared in examples 1-5 and comparative examples 1-2 was evaluated by measuring the contents of CO, HC, PM, and NOx in the exhaust gas from the inlet and outlet of the diesel engine exhaust gas treater.
TABLE 1
| Conversion of CO and HC% | PM purification rate% | The reduction rate of NOx% | Reduced ignition temperature | |
| Example 1 | 97.2 | 62.3 | 55.8 | 48℃ |
| Example 2 | 96.7 | 60.4 | 52.3 | 46℃ |
| Example 3 | 98.4 | 68.2 | 57.6 | 50℃ |
| Example 4 | 97.8 | 66.1 | 56.2 | 47℃ |
| Example 5 | 96.7 | 62.4 | 53.7 | 48℃ |
| Comparative example 1 | 96.3 | 48.6 | 31.2 | 42℃ |
| Comparative example 2 | 96.8 | 51.2 | 43.7 | 28℃ |
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are merely illustrative of the principles of the invention, but that various changes and modifications may be made without departing from the spirit and scope of the invention, which fall within the scope of the invention as claimed.
Claims (7)
1. The diesel engine tail gas oxidation catalyst is characterized in that cordierite honeycomb ceramic is used as a carrier, an adsorption layer is coated on the surface of a pore channel of the carrier, and a first oxidation catalyst layer and a second oxidation catalyst layer are coated on the adsorption layer; the concentration of the first active component in the first oxidation catalyst layer is in gradient decreasing change along the airflow direction on the surface of the carrier, and the concentration of the second active component in the second oxidation catalyst layer is in gradient increasing change along the airflow direction on the surface of the carrier; the second oxidation catalyst layer takes base metal oxide as a second active component, takes rare earth metal oxide and silicon dioxide as auxiliaries and takes zirconium-aluminum-silicon composite oxide as a load material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 1-3: 0.5-2: 20; the first oxidation catalyst layer takes precious metal as a first active component, takes rare earth metal oxide and silicon dioxide as auxiliaries, and takes zirconium-aluminum-silicon composite oxide as a load material, wherein the active components are as follows: auxiliary agent: the mass ratio of the load material is 1-3: 0.5-2: 20; the base metal oxide is at least one of an iron-based perovskite-type composite oxide, a manganese-based perovskite-type composite oxide, and a cerium-based perovskite-type composite oxide.
2. The diesel exhaust oxidation catalyst according to claim 1, wherein the mass ratio of the carrier, the adsorption layer, the first oxidation catalyst layer, and the second oxidation catalyst layer is 80 to 98: 1-15: 0.5-5: 0.5 to 5.
3. The diesel exhaust oxidation catalyst of claim 1, wherein the adsorbent layer is a cage silsesquioxane modified zeolite layer.
4. The diesel exhaust oxidation catalyst of claim 1, wherein the noble metal is at least one of platinum, palladium, and rhodium.
5. The diesel exhaust oxidation catalyst of claim 1, wherein the rare earth metal oxide is at least one of cerium oxide and lanthanum oxide.
6. The method of preparing a diesel exhaust oxidation catalyst according to claim 1, comprising the steps of:
s1: pretreatment of a carrier: placing a cordierite honeycomb ceramic carrier in a nitric acid solution for soaking for 3h, then washing with ultrasonic waves to be neutral, then drying in a drying oven at 110-120 ℃ for 1.5h, then placing in a muffle furnace for roasting at 600-800 ℃ for 2-3 h, and finally naturally cooling to obtain a pretreated cordierite honeycomb ceramic carrier;
s2: preparation of adsorption layer slurry: according to the mass ratio of zeolite, cage-type silsesquioxane to deionized water of 1-3: 0.5-2: 20, weighing the raw materials, uniformly ball-milling in a planetary ball mill, and controlling ball-milled particles D90 to be 5-15 mu m to prepare an adsorption layer slurry;
s3: preparation of a first oxidation catalyst layer slurry: according to the mass ratio of the noble metal, the rare earth metal oxide, the silicon dioxide, the zirconium-aluminum-silicon composite oxide and the deionized water of 1-3: 0.1-1.5: 0.1-1: 20: weighing the raw materials by 50, uniformly ball-milling in a planetary ball mill, and controlling the ball-milled particles D90 to be 1-5 mu m to prepare a first oxidation catalyst layer slurry;
s4: preparation of a second oxidation catalyst layer slurry: according to the mass ratio of base metal oxide, rare earth metal oxide, silicon dioxide, zirconium-aluminum-silicon composite oxide and deionized water of 1-3: 0.1-1.5: 0.1-1: 20: weighing the raw materials 50, uniformly ball-milling in a planetary ball mill, and controlling the ball-milled particles D90 to be 1-5 mu m to prepare second oxidation catalyst layer slurry;
s5: preparation of oxidation catalyst: dipping the cordierite honeycomb ceramic carrier obtained in the step S1 in the adsorption layer slurry prepared in the step S2, and finishing the dipping operation by an ultrasonic-assisted rotary evaporation method; blowing with compressed air and drying at 110 deg.c to constant weight; and taking out and placing the slurry into a sealed container, respectively arranging an inlet and an outlet at two ends of the sealed container along the airflow direction on the surface of the carrier, sequentially introducing the first oxidation catalyst layer slurry prepared in the step S3 and the second oxidation catalyst layer slurry prepared in the step S4 into the inlets, controlling the flow rate of the first oxidation catalyst layer slurry to gradually decrease from fast to slow, controlling the flow rate of the second oxidation catalyst layer slurry to gradually increase from slow to fast, depositing the slurry on the adsorption layer, blowing the slurry by compressed air again, drying the slurry to constant weight at 110 ℃, and finally roasting the slurry for 1 to 3 hours at 600 to 750 ℃ to obtain the oxidation catalyst with active ingredient concentration gradient change.
7. Use of an oxidation catalyst according to any one of claims 1 to 5 for the purification of diesel exhaust.
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